This method is for determining iron, nickel, vanadium, lead, copper, sodium, molybdenum, manganese, chromium, magnesium, tin, calcium, aluminum and zinc in crude petroleum, gas oils, fuel oils and jet fuels. Most of the elements can be determined within the concentration range of 0.02 to 200 mass-ppm when a 50-g sample of oil is ashed. Higher or lower concentrations can be determined by ashing appropriate-sized samples. The method is sufficiently flexible to add more elemental determinations if needed.